Coordinate position detection apparatus are known where a touch pen including an oscillator circuit emits a signal to allow a coordinate position to be detected.
JP Hei08(1996)-095701 A discloses a transparent digitizer that can also serve as a touch panel and can be switched between pen-input mode and finger-input mode. In this transparent digitizer-cum-touch panel, an analog multiplexer selects two line-shaped coordinate detection electrodes, and a balanced AC signal supplied to such a coordinate detection electrode is detected by a differential amplifier to determine the coordinate position.